The use of technologies permitting the use of hands with greater unbalance entails new problems:
the hands sliding on the tubes;
breakage of gear trains and/or rotors in electrical versions, in the event of a 5000 g shock.
This latter point is by far the most critical. In certain existing calibres, this type of breakage may occur in the event of a 5000 g shock, such as an accidental fall from the user's height.
Breakage means that the watch no longer functions, which strongly impacts the quality perceived by the user.
It is an object of the invention to prevent the gear trains and/or rotor from breaking by absorbing the energy from a shock, without affecting the design of the hands. Indeed, if a counterweight can be added to the hands to reduce their unbalance and thereby reduce the torque exerted during a large shock, this type of solution impairs the appearance of the hands desired by the manufacturers.
The energy from a shock must be absorbed to permit the use of hands with significant unbalance, which are increasingly common with the current trend of increasing the diameter of watches.
EP Patent No 1921516 in the name of the Swiss Watch Manufacturer ETA SA discloses a fastening for a silicon assembly element for use as a rotating element, in particular a hand or a toothed wheel. This assembly element includes two series of resilient structures etched into different layers of the plate in which the element is fabricated, to radially grip an arbour.
EP Patent No 1705533 in the name of PATEK PHILIPPE SA discloses an assembly of a silicon part on an arbour including a shoulder adjoining an axial stop member. The part includes a passage cooperating with the shoulder. The device further includes a washer with a hole fixed to the arbour so that the part is located between the stop member and the washer. The only possibility of protection against external stresses is provided by the elasticity of the silicon where the arbour is clamped.
CH Patent No 67295 in the name of BBC BROWN BOVERI & CIE discloses a wheel for heavy machinery including a toothed crown centred on a hub, with, just under the surface, a vibration or shock absorber device in the form of a tangentially mounted helical shock absorber spring, which is necessarily very bulky and unsuitable for horological applications.